BRITAIN has demanded serious explanations from Madrid after a Spanish warship entered Gibraltar’s waters yesterday and disrupted a Royal Navy military exercise.

Tension between the UK and Spain over Gibraltar has increased in the past year [PA]

We are raising this at a high level with the Spanish government and will be issuing a formal protest.

Foreign Office Spokesperson

Royal Navy chiefs were forced to suspend their session while the Gibraltar Squadron's patrol boat, HMS Sabre, shadowed the Spanish ship.

Warnings were issued to the vessel, which is said to have used a fake name and call sign, but it only left after radioing back that it was in Spanish waters.

Local reports suggesting special forces had been involved in the Royal Navy exercise were dismissed as wide of the mark.

However, the UK's ambassador to Spain, Simon Manley, who last year took over the position from BBC Newsnight presenter Jeremy Paxman's brother Giles, will raise the incursion at "a high level".

A Foreign Office spokesman said: "There was an incursion into British waters near Gibraltar by the Spanish Navy on 18 February, during a Royal Navy exercise. The exercise went ahead irrespective of this incursion.

"We are raising this at a high level with the Spanish government and will be issuing a formal protest.

"Neither this incident nor other incursions change the fact of UK sovereignty over British Gibraltar Territorial Waters."

There were long queues at Gibraltar's border with Spain last summer [PA]

Illegal Spanish incursions into Gibraltar waters have increased by more than 2,000 per cent since 2011 - with almost 500 incidents in the past year alone.

Figures released by the Foreign Office last month show Spanish state vessels illegally entered British-controlled waters 496 times in 2013 - up from 23 in 2011.

It is the highest number of incursions on record, even greater than when General Franco ruled Spain and blockaded Gibraltar.

Jim Dobbin, chairman of Parliament's All Party Group on Gibraltar, last month told Express Online he wanted to see a Royal Navy frigate permanently stationed at the Rock to deter further incursions.

Relations have been strained since the construction of an artificial reef by the Gibraltar government last year which the Spanish said interfered with their fishermen.

Madrid responded by imposing tighter border controls, leading to long delays at the frontier.

In November, a British diplomatic bag was opened and searched by Spanish Guardia Civil officers on the border with Gibraltar - an incident the Foreign Office described as a "serious infringement" of international diplomatic protocols.

A Ministry of Defence spokesman said: "The Royal Navy patrols and continues to challenge all unlawful incursions into British Gibraltar territorial waters by Spanish state vessels by issuing appropriate warnings.

"This forms an important part of Her Majesty's Government's commitment to uphold our sovereignty against unlawful incursions with a range of proportionate naval, police and diplomatic responses.

"There should be no doubt that the MoD remains absolutely committed to ensuring the defence and security of Gibraltar, its residents and British Gibraltar territorial waters."